Nav: Home

How hot is too hot for Earth-style life?

September 08, 2016


Nankai Trough, ~120 kilometers off the coast of Japan, where the ocean depth is 4.7 kilometers, and drilling will penetrate a further 1.2 kilometers beneath the seafloor, where layers of sediment and rock reach temperatures of 130°C (266°F), far above water's boiling point at Earth's surface.

Mission elements:
  • 31 researchers from 8 nations
  • World's largest, most stable scientific research ship
  • Helicopters to speed fresh samples from ship to shore
  • Super-clean lab on shore to prevent sample contamination
"Over the next 60 days, we have an unprecedented opportunity to learn more about when temperatures become too hot for microbial life to survive below the seafloor," said Dr. Verena Heuer, expedition co-chief scientist.

The ocean floor is teeming with worms (nematodes) and other eukaryotic organisms, which live in sediments together with a myriad of microbes representing the three domains of life (Archaea, Bacteria, and Eukaryotes). As the sediments get deeper and warmer, microbial forms become less abundant.

During this expedition, scientists will look for as few as 100 cells per cm3, or roughly the equivalent of 100 sand grains floating in an Olympic-sized swimming pool. Finally, in the deepest samples retrieved on this research cruise, the team expects samples beyond the borders of life where current knowledge predicts that no living cells persist. This is the first attempt to explore this boundary, the biotic fringe, in detail. The team aims to determine whether it is sharp, diffuse, or exists at all.

With scientists working simultaneously on land and at sea, the research is part of the International Ocean Discovery Program's (IODP) Expedition 370: T-Limit of Deep Biosphere off Muroto, and targets many of the science goals of the Deep Carbon Observatory, an international multidisciplinary research program investigating the role of deep carbon in planetary function.

Scientists will share their experiences during the cruise via blogs at and on the Expedition 370 website,

Interested individuals can engage with the mission by guessing the temperature limit of life under the seafloor in the Deep Carbon Observatory's "How hot is too hot?" contest at

Limits to life

"We know the microbial biomass living under the seafloor compares to that found in the global ocean," explained co-chief scientist Dr. Fumio Inagaki. "Yet, there are many unknowns about this mass of life deep below the seafloor, including its diversity, borders, and the factors limiting its survival."

Previous research at hot vents in the seafloor suggests life can survive temperatures a little above 120°C. DNA molecules, at least under surface conditions, lose their integrity at temperatures between 120-140°C, and without DNA, life as we know it cannot exist. Yet we know that carbon, hydrogen, and other essential building blocks of life are plentiful under even more extreme temperatures deep inside Earth.

"We have the extraordinary opportunity to explore the depth at which sediments and rocks become too hot for life, even for microbes that can live at temperatures greater than 85°C," said co-chief scientist Heuer. "The gradual increase in temperature from approximately 30°C to 130°C in the sampled sediments will give us the opportunity to explore how microbial life changes with increasing temperatures and ultimately ceases to exist. Is this lower boundary of the subseafloor's habitable zone like a rigid brick wall or is it like a leaky fence?"

Simultaneous shipboard and land-based science

On 12 September 2016, an international team of 25 researchers will board the drilling vessel (D/V) Chikyu, the world's largest scientific research vessel, in Shimizu Port in Shizuoka, Japan, to begin a 60-day quest to determine the limits of life below the ocean's floor. Working with six additional shore-based scientists, the team will attempt to define the temperature limits to deep life in marine sediments and to clarify key factors, including pressure, limiting Earth's underground habitable zone.

A unique aspect of this endeavor involves investigations occurring simultaneously onboard the Chikyu and on land at the Kochi Core Center. For the first time, helicopters will speed fresh core samples from the Chikyu to the state-of-the-art research facilities in the Kochi Core Center. There, members of the shore-based science team, led by co-chief scientist Dr. Yuki Morono, will analyze samples to determine the geochemical and microbiological characteristics of the sediments, and painstakingly count minuscule and sparse cells.

The team also will use next-generation DNA sequencing technology to determine which organisms can survive in deep subseafloor sediments and their ancestry. Genetic data like these will provide clues showing how resident microbes adapt to such extreme environments.

Explained Morono, "Looking for life in core samples is like looking for a needle in a haystack. At the surface, the sediments are teeming with microbial cells, but in samples from deeper in the core, the cells become far more sparse."

The state-of-the-art Japanese drilling vessel Chikyu will travel to the central Nankai Trough, ~120 kilometers off the coast of Japan where the ocean is 4.7 kilometers deep, and drill a further 1.2 kilometers beneath the ocean's floor to collect sediment and rock cores. The total distance from the ocean's surface to the target sample depth is equivalent to the height of 18 Eiffel Towers. Carefully selected samples from those cores then will be sent on a one-hour helicopter ride for further investigation by the shore-based science team. The team will search for life within the cores at the super-clean laboratory space of the Kochi Core Center, which is run jointly by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and Kochi University.

When the 60-day mission ends around 10 November, the shipboard and shore-based investigators will unite at the Kochi Core Center for a day of debriefing. Then the land-based team will spend a further two weeks analyzing samples.

"This expedition is as complex as a mission to outer space might be," explained Dr. Kai-Uwe Hinrichs, MARUM, University of Bremen, and lead author of the scientific proposal behind the expedition. "It requires the technology to 'land' the coring bit on the right spot in over 4 kilometer-deep water, drill through ancient ocean sediments to collect samples far below the ocean floor, bring them back onboard intact, then transport them by helicopter to the super-clean geomicrobiology laboratory to ensure no contamination. Like a space mission, this expedition is fraught with complexity, danger, and vast opportunity for discovery."

The Nankai Trough off Cape Muroto offers unique conditions where temperatures can approach ~130°C as cores are collected from 1.2 kilometers depth below the seafloor. Based on previous data from deep-sea hydrothermal vents, researchers expect the upper limit of life in the seafloor near 120°C. The hottest life currently catalogued on Earth includes Geogemma barossii, a single-celled organism thriving in hydrothermal vents on the sea floor. Its cells, tiny microscopic spheres, grow and replicate at 121°C. Scientists found the organism, also known as strain 121, in a sample collected during a 2003 expedition to the Juan de Fuca Ridge off the northwest USA coast and named it after Deep Carbon Observatory scientist John Baross (University of Washington, USA), who provided the sample. At pressure characteristic of about 2000-4000 meters deep (20-40 megapascals), scientists reported cell growth and methane production of a competitor for most heat tolerant organism, Methanopyrus kandleri strain 116, up to 122°C.

The Trough is located on the Eurasian plate, where heat flow is particularly high, near its boundary with the subducting young, hot Philippine Sea tectonic plate. At the targeted site, the geothermal gradient is about four times steeper than elsewhere in the Pacific Ocean. Reaching these temperatures in other areas would require collecting cores from ~4 kilometers below the seafloor, rather than 1.2 kilometers as planned.

Researchers found the site in Nankai Trough 15 years ago but now return with a renewed purpose and more advanced technologies, coupled with analysis capabilities of the Kochi Core Center and other top laboratories around the world. Investigators will also consider existing data to learn how cell concentrations drop to zero, or if life continues at a slower pace or with different forms of microbes with different energy needs.

Three co-chief scientists are leading the mission: Drs. Verena Heuer (MARUM, University of Bremen), Fumio Inagaki (Kochi Institute for Core Sample Research/Research and Development Center for Ocean Drilling Science, JAMSTEC), and Yuki Morono (Kochi Institute for Core Sample Research, JAMSTEC). The co-chief scientists, Hinrichs, and many others on the science team are members of the Deep Carbon Observatory.

IODP Expedition 370 will address some of the Deep Carbon Observatory's fundamental objectives regarding deep life, which include mapping the abundance and diversity of subsurface marine microorganisms in time and space as a function of their genomic and biogeochemical properties, and their interactions with deep carbon.
The Deep Carbon Observatory (DCO) is an international network of about 900 scientists investigating the quantities, movements, forms, and origins of carbon in deep Earth. Kai-Uwe Hinrichs (MARUM, University of Bremen, Germany) and Mitchell Sogin (Marine Biological Laboratory, Woods Hole, USA) co-chair the Deep Life community within the DCO. The Alfred P. Sloan Foundation (New York) provides core support for the DCO.

IODP is the International Ocean Discovery Program, an international marine research collaboration that explores Earth's history and dynamics using ocean-going research platforms to recover data recorded in seafloor sediments and rocks and to monitor subseafloor environments. IODP depends on facilities funded by three platform providers with financial contributions from five additional partner agencies. Together, these entities represent 25 nations whose scientists are selected to staff IODP research expeditions conducted throughout the world's oceans.

JAMSTEC is the Japan Agency for Marine-Earth Science and Technology, which contributes to the advancement of academic research and the improvement of marine science and technology through fundamental marine-related research and development for the benefit of the peace and human welfare. JAMSTEC's Center for Deep Earth Exploration (CDEX) is an implementing organization for the International Ocean Discovery Program (IODP), managing D/V Chikyu as one of three IODP platforms within a framework established by the IODP member countries.

MARUM is the Center for Marine Environmental Sciences at the University of Bremen in Germany. MARUM aims at understanding the role of the oceans in the Earth system by employing state-of-the-art methods. It examines the significance of the oceans within the framework of global change, quantifies interactions between the marine geosphere and biosphere, and provides information for sustainable use of the ocean.

More information:

About the expedition -

AAbout the Deep Carbon Observatory -


AAbout D/V Chikyu -

AAbout MARUM -

AAbout the International Ocean Discovery Program -


Dr. Katie Pratt
1 401 874 6146
1 401 536 8813 (mobile)

Darlene Trew Crist
1 207 315 1976 (mobile)

Deep Carbon Observatory

Related Carbon Articles:

Can wood construction transform cities from carbon source to carbon vault?
A new study by researchers and architects at Yale and the Potsdam Institute for Climate Impact Research predicts that a transition to timber-based wood products in the construction of new housing, buildings, and infrastructure would not only offset enormous amounts of carbon emissions related to concrete and steel production -- it could turn the world's cities into a vast carbon sink.
Investigation of oceanic 'black carbon' uncovers mystery in global carbon cycle
An unexpected finding published today in Nature Communications challenges a long-held assumption about the origin of oceanic black coal, and introduces a tantalizing new mystery: If oceanic black carbon is significantly different from the black carbon found in rivers, where did it come from?
First fully rechargeable carbon dioxide battery with carbon neutrality
Researchers at the University of Illinois at Chicago are the first to show that lithium-carbon dioxide batteries can be designed to operate in a fully rechargeable manner, and they have successfully tested a lithium-carbon dioxide battery prototype running up to 500 consecutive cycles of charge/recharge processes.
How and when was carbon distributed in the Earth?
A magma ocean existing during the core formation is thought to have been highly depleted in carbon due to its high-siderophile (iron loving) behavior.
New route to carbon-neutral fuels from carbon dioxide discovered by Stanford-DTU team
A new way to convert carbon dioxide into the building block for sustainable liquid fuels was very efficient in tests and did not have the reaction that destroys the conventional device.
How much carbon the land can stomach with more carbon dioxide in the air
Researchers from 28 institutions in nine countries succeeded in quantifying carbon dioxide fertilization for the past five decades, using simulations from 12 terrestrial ecosystem models and observations from seven field carbon dioxide enrichment experiments.
'Charismatic carbon'
According to the Intergovernmental Panel on Climate Change (IPCC), addressing carbon emissions from our food sector is absolutely essential to combatting climate change.
Extreme wildfires threaten to turn boreal forests from carbon sinks to carbon sources
A research team investigated the impact of extreme fires on previously intact carbon stores by studying the soil and vegetation of the boreal forest and how they changed after a record-setting fire season in the Northwest Territories in 2014.
Can we still have fun if the UK goes carbon neutral?
Will Britain going carbon neutral mean no more fun? Experts from the University of Surrey have urged local policy makers to put in place infrastructure that will enable people to enjoy recreation and leisure while keeping their carbon footprint down.
Could there be life without carbon? (video)
One element is the backbone of all forms of life we've ever discovered on Earth: carbon.
More Carbon News and Carbon Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at